Prepare the dressing by whisking together the sour cream,
mayonnaise, milk, garlic, Worcestershire sauce, sugar,
white pepper and cayenne pepper. Store in an air−tight container
and refrigerate.
Prepare the salad in a large bowl by combining the lettuce, onion,
oranges and mushrooms. Add enough dressing to coat and toss.
Sprinkle with salt and pepper and add croutons if desired.